title: Detection of primary sites in unknown primary tumors using FDG-PET or FDG-PET/CT.
abstract: BACKGROUND
  Carcinoma of unknown primary tumors (CUP) is present in 0.5%-9% of all patients with malignant neoplasms; only 20%-27% of primary sites are identified before the patients die. Currently, 18F-fluorodeoxy-glucose positron-emission tomography (18F-FDG PET) or PET combined with computed tomography (PET/CT) is widely used for the diagnosis of CUP. However, the diagnostic yield of the primary site varies. The aim of this study was to determine whether PET or PET/CT has additional advantages over the conventional diagnostic workup in detecting the primary origin of CUP.
  
  
  RESULTS
  Twenty patients with unknown primary tumors that underwent PET or PET/CT were included in this study. For all patients, the conventional diagnostic workup was unsuccessful in detecting the primary sites. Among 20 patients, 11 had PET scans. The remaining nine patients had PET/CT. In all 20 patients, neither the PET nor PET/CT identified the primary site of the tumor, including six cases with cervical lymph node metastases. The PET and PET/CT revealed sites of FDG uptake other than those associated with known metastases in seven patients, but these findings did not influence patient management or therapy. Two patients had unnecessary invasive diagnostic procedures due to false positive results on the PET or PET/CT.
  
  
  CONCLUSIONS
  Although it is inconclusive because of small sample size of the study, the additional value of PET or PET/CT for the detection of primary sites in patients with CUP might be less than expected; especially in patients that have already had extensive conventional diagnostic workups. Further study is needed to confirm this finding.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and Lung Institute of Medical Research Center, Seoul National University College of Medicine, Seoul, Korea. sangmin2@snu.ac.kr.
authors.forename: Jong Sun
authors.initials: JS
authors.lastname: Park
authors.forename: Jae-Joon
authors.initials: JJ
authors.lastname: Yim
authors.forename: Won Jun
authors.initials: WJ
authors.lastname: Kang
authors.forename: June-Key
authors.initials: JK
authors.lastname: Chung
authors.forename: Chul-Gyu
authors.initials: CG
authors.lastname: Yoo
authors.forename: Young Whan
authors.initials: YW
authors.lastname: Kim
authors.forename: Sung Koo
authors.initials: SK
authors.lastname: Han
authors.forename: Young-Soo
authors.initials: YS
authors.lastname: Shim
authors.forename: Sang-Min
authors.initials: SM
authors.lastname: Lee